Chap. VI] 



ANIMALS 



137 





Thus prepared, the now shapeless little masses are worked up into a. 

 coarsely porous spongy mass which fills the interior of the nest and 

 forms the fungus-garden (Fig. 73). The little masses, the initial green 

 colour of which changes first to bluish-black and finally to yellowish- 

 brown, are traversed in all directions and bound together by fine mycelial 

 threads. On closer inspection, innumerable little white bodies, at the 

 most -5 mm. in diameter, may also be seen ; they spring laterally from 

 the mycelial threads and are termed by Moller 'kohlrabi-clumps' (Fig. 

 74). They consist of an agglomeration of short branches with node- 

 like or globular swollen ends and very rich protoplasmic contents. The 

 1 kohlrabi-clumps ' arc the most important if not the sole food of the ants, 

 and represent a new structure, which has arisen as a result of artificial 

 selection exercised by the ants. 



The ' kohlrabi-clumps ' appear very early in the fresh masses and 

 then disappear, when these assume a brown colour. Alf. Moller has, 

 by ingenious experiments, revealed 

 the whole workings of the ants in 

 their fungus-gardens, and has shown 

 how the tiniest female workers keep 

 off all foreign organisms, so that 

 without further trouble the little 

 masses can be used for pure cul- 

 tures, and how the ants, by indus- 

 triously biting off the subaerial 

 threads, prevent the vegetative 

 sprouting which will be described 

 further on. He has also directly 

 observed, in numerous cases, the 

 actual eating of the ' kohlrabi- 

 clumps' and has proved that in their absence the ants die of starvation. 



The fungus, as a rule, remains in the purely vegetative condition 

 that has just been described. Only exceptionally, and under unknown 

 conditions, do large pileate sporophores of a purely agaric type develop 

 from the mycelium and crown the top of the ants' nest, a feature that 

 is all the more striking because large pileate fungi are rare in tropical 

 rain-forests. Such discoveries have made it possible for Alf. Moller to 

 determine exactly the systematic position of the fungus, and to describe 

 it as a new species of the genus Rozites, R. gongylophora, Moll. 



The four species of Atta that occur near Blumenau cultivate the same 

 species of fungus, which is never found outside the ants' nests. We have 

 therefore here a highly developed case of reciprocal adaptation between 

 unlike organisms. 



The removal of the ants from the fungus-garden results, after a few 





Fig. 74. 'Kohlrabi-clumps' of Rozites gongy- 

 lophora, Moll., the fungus of the South Brazilian 

 species of Atta. Magnified 150. After Alf. Moller. 



